It is expected that optical communications will significantly gain in importance as they allow for further increasing the communication speed and bandwidth for microscopic applications, such as chips, and allow further reduction of the footprint of such applications. To transform an electric signal to an optical signal an optical modulator is used, for example a resonant electro-optic modulator as described in Low voltage, Low-Loss, Multi-Gb/s Silicon Micro-Ring Modulator based on a MOS Capacitor by Joris Van Campenhout, Marianne Pantouvaki, Peter Verheyen, Shankar Selvaraja, Guy Lepage, Hui Yu, Willie Lee, Johan Wouters, Danny Goossens, Myriam Moelants, Wim Bogaerts and Philippe Absil in “The Optical Fiber Communication Conference and Exposition (OFC) and The National Fiber Optic Engineers Conference (NFOEC) 2012”, United States, p.OM2E (2012).
However, although such modulators may have very good characteristics with respect to conversion speed, power usage and footprint, their output for a given wavelength depends relatively heavily on their operating temperature.
Active wavelength control of Silicon microphotonic resonant modulators by Anthony L. Lentine, W. A. Zortman, D. C. Trotter and Michael R. Watts published in “Optical Interconnects Conference, 2012 IEEE” describes a thermally stabilised resonant electro-optic modulator for optical communication purposes of binary data. The modulator comprises a resonant electro-optic modulator unit. The resonant electro-optic modulator unit comprises a first ring-shaped waveguide and a second longitudinal waveguide adjacent to the first waveguide. The thermally stabilised resonant electro-optic modulator further comprises a voltage unit for applying a first and a second voltage over the ring-shaped waveguide, a light sensor for determining the intensity of the light transmitted through the second waveguide after having passed along the first waveguide, a thermal stabilisation unit for adjusting the temperature of the first waveguide and a temperature control unit for controlling the thermal stabilisation unit in response to a signal representing the intensity measured by the light sensor. The first and the second waveguides are arranged such that light with a wavelength transmitted through the second waveguide is differently attenuated by resonance in the first waveguide by application of either the first or the second voltage allowing a higher throughput of light with that wavelength through the second waveguide along the first waveguide at the first voltage, thus representing a 1-bit, than at the second voltage, thus representing a 0-bit. A third waveguide is provided adjacent to the first waveguide, the first and the third waveguides being arranged such that light transmitted through the first waveguide is attenuated by resonance in the third waveguide. Such a third waveguide usually is called a drop port. The light sensor is provided to measure the intensity of the light transmitted through the second waveguide as a result of attenuation into the third waveguide from the first waveguide. Based on the measured intensity by the light sensor, a decision is made whether the intensity of the light as measured by the light sensor represents a 0-bit or a 1-bit. Further the thus measured bits are compared with the original bits as originally supplied to the modulator unit, more in particular the first waveguide, in the form of the first and the second voltage. Depending on the difference in between the measured bits and the original bits, the temperature control unit controls the thermal stabilisation unit.
However, in such configuration an additional transformation is needed in the form of the decision whether the output of the light sensor represents a 0-bit or a 1-bit. This additional transformation requires additional electrical components which are often relatively complicated, require additional power and make the thermally stabilised resonant electro-optic modulator more prone to malfunctions. Moreover, in order to achieve high data transmission speed, high speed computation components are for exampled required for making the decision whether the output of the light sensor represents a 0-bit or a 1 bit or for example for comparing the bits as measured and the bits as originally supplied to the modulator unit.